What is the difference between a gas and a vapour? I remember one of my lecturers saying that there was a slight technical difference, but i dont think he ever did explain it because it was not important for what we were doing. I did a quick google search and one of the results i found was that 'vapour' refers to a substance in the gaseous phase even though under normal conditions it does not exist as a gas i.e. the vapour pressure of a liquid/solid at standard conditions, whereas a 'gas' refers to a gaseous substance that does naturally occur as a gas under standard conditions, such as oxygen or nitrogen. Is this distinction correct? The source wasn't the most reliable of sources, so it would be nice to get some validation Thanks, Dan.